In these years, in a case of treating a tooth affected by a periodontal disease, an endosseous dental implant method has been employed in which the affected tooth is extracted and then an artificial tooth root is embedded into the extracted portion of a jawbone. In this case, since a part of the jawbone is affected by the periodontal disease, so that the jawbone part is lost, the artificial tooth root could not be supported sufficiently. For this reason, in order to regenerate the lost portion of the jawbone, various methods have been considered.
As one of the methods, a calcium phosphate based bone prosthetic material in a granular or block shape is used. However, since a dense sintered body and dense phosphate glass (bioglass) are used as the bone prosthetic materials in this method, these materials are hard to be absorbed into a living body. For this reason, a long time period is required to completely replace the bone prosthetic material with an autologous bone.
In addition, there are many kinds of calcium phosphate such as hydroxyapatite (HAP) and tricalcium phosphate (TCP). Because the hydroxyapatite (HAP) of them has biocompatibility but is hard to be absorbed into a living body, there is a possibility that the hydroxyapatite remains in the body after treatment for a long time period. Meanwhile, since tricalcium phosphate (TCP) has bioresorbable, it does not remain in the body after the treatment by being displaced by new bone tissue and accordingly can be easily handled. In addition, there are two kinds of tricalcium phosphate of α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP), and since having higher bioresobability than that of β-TCP, α-TCP is absorbed into the living body more quickly.
When granular material formed of α-TCP or β-TCP is embedded into a bone defect portion, the granular material is absorbed by osteoclastic cells and simultaneously a bone tissue is regenerated around the granular material by osteoblast cells. In this manner, the granular material is gradually replaced with the autologous bone. As described above, α-TCP and β-TCP are replaced with the bone tissue by cells. However, it is desirable that α-TCP and β-TCP are gradually absorbed in association with generation of a new bone without being absorbed immediately. When having a short replacement time period, α-TCP is absorbed before the bone tissue is sufficiently generated, and accordingly there is a possibility that α-TCP cannot serve as a scaffold of the generation of bone. In addition, the replacement reaction occurs on a surface of the granular material contacting cells, and accordingly a surface structure and an extent of a surface area in the granular material will be important factors.
As shown in JP 2006-122606A, the inventors of the present application focused attention on characteristics of α-TCP or β-TCP, and proposed a bone prosthetic material whose inner portion is formed of β-TCP and whose surface portion is formed of α-TCP, in order to reduce a regeneration period as much as possible.
Additionally, as a technique focusing on a role of the granular material, JP-A-Heisei 5-237178 proposes a bone prosthetic material formed of calcium phosphate based ceramics having a dense portion and a porous portion. In this bone prosthetic material, a cellular porous portion is produced by use of foaming agent mixed into this material. It is not described how the osteoblast cells enter the porous portion, and also is not clarified how the existence of the porous portion influences the regeneration period of bone.
As described above, a technique for treating and regenerating a defected bone in a short time is not yet proposed actually.
From this reason, a regeneration mechanism of bone has been studied and analyzed, and a knowledge described below has been found. Specifically, existence of osteoblast cells is required in the regeneration of bone, and blood is essential to keep the existence of the osteoblast cells. The knowledge shows that if the bone prosthetic material fills a bone defect portion, and the osteoblast cells and the blood can be sufficiently supplied to a surface of the bone prosthetic material (by a blood capillary and an arteriole vessel), the regeneration of bone can be realized in a short time.